What are the changes in the variable region of immunoglobulins?
Maximum density of microfilariae in blood is reported to be between -
What is the cause of rabies in wild animals?
The outer covering of diatoms is made of?
Which gene of Hepatitis B virus (HBV) is most commonly associated with mutations causing antiviral drug resistance?
Which of the following statements about malaria transmission is correct?
Amoebic liver abscess can be diagnosed by demonstrating-
Who discovered the bacterium Treponema pallidum?
Who discovered the bacterium Mycobacterium tuberculosis, which causes tuberculosis?
Which of the following bacteria does not exhibit bipolar staining?
NEET-PG 2013 - Microbiology NEET-PG Practice Questions and MCQs
Question 71: What are the changes in the variable region of immunoglobulins?
- A. Isotype
- B. Epitope
- C. Allotype
- D. Idiotype (Correct Answer)
Explanation: ***Idiotype*** - **Idiotype** refers to the unique set of antigenic determinants in the **variable region** of an antibody molecule, specifically within the **hypervariable regions (complementarity-determining regions, CDRs)**. - These unique determinants allow antibodies to recognize specific antigens and are generated by the specific **V(D)J gene rearrangements** in B cells. *Isotype* - **Isotype** refers to the constant region of an antibody, determining its class (e.g., **IgG, IgM, IgA, IgD, IgE**). - This region defines the antibody's effector functions and has nothing to do with the antigen-binding variability. *Allotype* - **Allotype** refers to minor genetic variations within the **constant region** of an antibody molecule within a species. - These variations are due to different alleles inherited from parents and are not associated with the variable region that binds to antigens. *Epitope* - An **epitope** is the specific part of an **antigen** that an antibody or T-cell receptor recognizes and binds to. - It is a feature of the antigen, not a change within the variable region of the immunoglobulin itself.
Question 72: Maximum density of microfilariae in blood is reported to be between -
- A. 9 pm to 11 pm
- B. 11 pm to 2 am (Correct Answer)
- C. 8 pm to 10 pm
- D. 2 am to 5 am
Explanation: ***11 pm to 2 am*** - This period aligns with the **nocturnal periodicity** of *Wuchereria bancrofti* and *Brugia malayi* microfilariae, which are the most common causes of filariasis. - The microfilariae migrate to the **peripheral circulation** during these hours, making it the optimal time for blood smear collection for diagnosis. *9 pm to 11 pm* - While still within the active period for microfilarial migration, the **peak density** is generally observed slightly later. - Blood drawn during this time might show microfilariae, but in lower concentrations compared to the peak. *8 pm to 10 pm* - This timing is generally a little too early to consistently capture the **highest microfilarial load** in nocturnal periodic infections. - The microfilariae are still in the process of migrating from deeper tissues to the peripheral blood. *2 am to 5 am* - By this time, the microfilarial density in the peripheral blood of **nocturnal periodic species** usually starts to decline. - While some microfilariae may still be present, the count would likely be lower than during the earlier peak hours.
Question 73: What is the cause of rabies in wild animals?
- A. Wild-type rabies virus (Correct Answer)
- B. Laboratory passage in rabbits
- C. Fatal encephalitis within 6 days
- D. Negri bodies are not observed
Explanation: ***Wild-type rabies virus*** - Rabies in wild animals is caused by infection with the **wild-type rabies virus (Lyssavirus)**, which is maintained in specific wildlife reservoirs. - Rabies virus is a **neurotropic RNA virus** belonging to the family *Rhabdoviridae*. - This virus is transmitted through the saliva of an infected animal, typically via a **bite**. *Laboratory passage in rabbits* - **Laboratory passage in animals**, particularly rabbits, was a historical *method for attenuating the rabies virus* to develop vaccines (e.g., Pasteur's vaccine), not a cause of infection in wild animals. - Attenuated viruses are **less virulent** and do not represent the primary cause of naturally occurring rabies in wildlife. *Fatal encephalitis within 6 days* - This statement describes a **rapid progression of the disease**, which can occur, but it is a *consequence of infection*, not the cause itself. - The incubation period for rabies can vary significantly in animals, from days to months, depending on the **site of the bite** and **viral load**. *Negri bodies are not observed* - **Negri bodies** are *pathognomonic microscopic inclusions* found in the brain cells of animals infected with rabies. - Their *absence* would generally suggest that the animal does not have rabies, making this an incorrect statement about the disease's characteristics.
Question 74: The outer covering of diatoms is made of?
- A. Magnesium
- B. Silica (Correct Answer)
- C. Hydrocarbons
- D. None of the options
Explanation: ***Correct: Silica*** - The cell walls of diatoms are primarily composed of **hydrated amorphous silica (SiO2·nH2O)**. - This rigid, intricate outer covering is known as a **frustule**, which provides structural support and protection. - Diatoms are uniquely characterized by their intricate silica cell walls, making them easily identifiable under microscopy. *Incorrect: Magnesium* - **Magnesium (Mg)** is an important metal and a component of chlorophyll, essential for photosynthesis. - While diatoms do contain magnesium for metabolic processes, it is not the primary structural component of their outer covering. *Incorrect: Hydrocarbons* - **Hydrocarbons** are organic compounds consisting entirely of hydrogen and carbon, commonly found in fossil fuels. - Diatom cell walls are inorganic (mineral-based), not organic hydrocarbon structures. *Incorrect: None of the options* - This option is incorrect because **silica** is listed among the options and is the correct answer. - Diatom frustules are definitively composed of silica.
Question 75: Which gene of Hepatitis B virus (HBV) is most commonly associated with mutations causing antiviral drug resistance?
- A. X gene
- B. S gene
- C. C gene
- D. P gene (Correct Answer)
Explanation: ***P gene*** - The **P gene** (polymerase gene) of HBV encodes the viral reverse transcriptase which is essential for viral replication. - Mutations in the P gene can lead to **antiviral drug resistance**, particularly to nucleos(t)ide analogues. *X gene* - The **X gene** encodes the X protein (HBx), a **transcriptional transactivator** involved in viral replication and pathogenesis. - While important for viral function, it is not the primary target for antiviral therapy, and mutations are less frequently associated with drug resistance. *S gene* - The **S gene** encodes the **surface antigens (HBsAg)**, which are crucial for viral entry and immune evasion. - Mutations in the S gene can lead to **vaccine escape mutants** or alter HBsAg detection, but not directly responsible for antiviral resistance. *C gene* - The **C gene** encodes the **core protein (HBcAg)** and the precore protein (HBeAg). - These proteins are involved in **viral particle assembly** and immune modulation, but mutations in this gene are not typically associated with resistance to antiviral drugs.
Question 76: Which of the following statements about malaria transmission is correct?
- A. Individuals harboring gametocytes can transmit malaria. (Correct Answer)
- B. P. vivax always completely fills the infected RBC with schizonts.
- C. Malaria can only be transmitted through blood transfusions.
- D. All stages of P. falciparum are commonly seen in peripheral blood smears.
Explanation: ***Individuals harboring gametocytes can transmit malaria.*** - **Gametocytes** are the sexual stage of the malaria parasite that circulate in the human bloodstream and are infectious to mosquitos. - When an *Anopheles* mosquito feeds on an infected human, it ingests these gametocytes, allowing the parasite's life cycle to continue in the mosquito vector, leading to transmission. *P. vivax always completely fills the infected RBC with schizonts.* - While *P. vivax* does infect **reticulocytes** (young RBCs) and can enlarge them, the **schizonts** typically occupy a significant portion but not always completely fill the host cell. - The infected RBCs are often enlarged to about 1.5 to 2 times their normal size and contain numerous **Schüffner's dots**. *Malaria can only be transmitted through blood transfusions.* - The primary mode of malaria transmission is through the bite of an **infected female *Anopheles* mosquito**. - While **blood transfusions** can transmit malaria, it is a less common and secondary route compared to vector-borne transmission. *All stages of P. falciparum are commonly seen in peripheral blood smears.* - In *P. falciparum* infections, only the **ring forms** and **gametocytes** are commonly observed in the peripheral blood smear. - The more mature asexual stages (trophozoites and schizonts) typically sequester in the capillaries of internal organs, where they are not readily visible in peripheral circulation.
Question 77: Amoebic liver abscess can be diagnosed by demonstrating-
- A. Trophozoites in the pus (Correct Answer)
- B. Trophozoites in the feces
- C. Cysts in the pus
- D. Cysts in the liver
Explanation: ***Trophozoites in the pus*** - **Amoebic liver abscesses** are caused by the invasive **trophozoite stage** of *Entamoeba histolytica*. - Demonstrating **trophozoites** in the characteristic **'anchovy paste' pus** aspirated from the abscess cavity is diagnostic. *Cysts in the pus* - **Cysts** are the **infective stage** of *Entamoeba histolytica* and are typically found in the **feces**, not in an abscess. - Cysts are responsible for transmission and survival outside the host, but they do not cause invasive disease. *Cysts in the liver* - The disease in the liver is caused by **trophozoites**, which invade the intestinal wall and then spread to the liver. - **Cysts** are never found within the liver parenchyma or abscesses. *Trophozoites in the feces* - While **trophozoites** can be found in the feces during acute amoebic dysentery, their presence alone does not confirm a liver abscess. - Furthermore, **trophozoites** are fragile and often difficult to detect in stool samples, especially once the stool has cooled.
Question 78: Who discovered the bacterium Treponema pallidum?
- A. Robert Koch
- B. Twort
- C. Ellerman
- D. Fritz Schaudinn and Erich Hoffmann (Correct Answer)
Explanation: ***Fritz Schaudinn and Erich Hoffmann*** - **Fritz Schaudinn** was a German zoologist, and **Erich Hoffmann** was a German dermatologist; they jointly discovered **Treponema pallidum** in **1905**. - Their discovery of the spirochete was a crucial step in understanding the etiology of **syphilis**. *Robert Koch* - **Robert Koch** is renowned for identifying the causative agents of **tuberculosis**, **cholera**, and **anthrax**. - He developed Koch's postulates, a fundamental set of criteria for establishing the causal relationship between a microbe and a disease. *Twort* - **Frederick Twort** was a British bacteriologist who is credited with the discovery of **bacteriophages** in **1915**. - His work involved examining transparent areas in bacterial cultures, leading to the identification of lytic viruses that infect bacteria. *Ellerman* - **Vilhelm Ellerman** was a Danish pathologist known for his work in **hematology** and **virology**. - Alongside **Olaf Bang**, he demonstrated that avian leukemia (erythroleukemia) could be transmitted by a filterable agent, indicating a viral etiology for some cancers.
Question 79: Who discovered the bacterium Mycobacterium tuberculosis, which causes tuberculosis?
- A. Jenner
- B. Louis Pasteur
- C. Robert Koch (Correct Answer)
- D. Lister
Explanation: ***Robert Koch*** - **Robert Koch** discovered the bacterium *Mycobacterium tuberculosis* in **1882**, identifying its role as the causative agent of tuberculosis. - His work was crucial in establishing the germ theory of disease and earned him the Nobel Prize in Physiology or Medicine in 1905. *Louis Pasteur* - **Louis Pasteur** was a pioneer in microbiology, known for his work on **pasteurization**, **vaccinations** (e.g., rabies and anthrax), and disproving spontaneous generation. - While he made significant contributions to understanding infectious diseases, he did not discover *Mycobacterium tuberculosis*. *Lister* - **Joseph Lister** was a British surgeon who revolutionized surgery by introducing **antiseptic techniques** using carbolic acid to prevent infections. - His contributions were fundamental to reducing mortality rates from surgical infections, but he did not discover the tuberculosis bacterium. *Jenner* - **Edward Jenner** is famous for developing the **smallpox vaccine**, which was a groundbreaking achievement in immunology and public health. - His work, though vital for preventing infectious diseases, predates and is unrelated to the discovery of *Mycobacterium tuberculosis*.
Question 80: Which of the following bacteria does not exhibit bipolar staining?
- A. Haemophilus influenzae (Correct Answer)
- B. Yersinia pestis
- C. Calymmatobacterium granulomatis
- D. Francisella tularensis
Explanation: ***Haemophilus influenzae*** - *Haemophilus influenzae* is a **pleomorphic coccobacillus** that typically stains uniformly and does not exhibit characteristic **bipolar staining**. - Its presence is often identified by Gram stain showing small, Gram-negative rods, but without the distinctive safety pin appearance. *Calymmatobacterium granulomatis* - *Calymmatobacterium granulomatis* (now *Klebsiella granulomatis*) is known to exhibit **bipolar staining**, often described as a **"safety pin" appearance**, especially in tissue smears from granuloma inguinale lesions. - This characteristic staining is due to the concentration of stain at the ends of the rod-shaped bacteria. *Yersinia pestis* - *Yersinia pestis*, the causative agent of plague, is classically described as having **bipolar staining**, giving it a distinctive **"safety pin" appearance** under a microscope. - This finding is a key diagnostic feature, particularly when observed in Gram-stained smears of clinical samples. *Francisella tularensis* - *Francisella tularensis* is a small, Gram-negative coccobacillus that is known to exhibit **bipolar staining**, though it may be less prominent than in *Yersinia pestis*. - This characteristic can assist in the microscopic identification of the bacterium, which causes tularemia.